System and method for controlling and diagnosing passive storage devices in exhaust aftertreatment systems

Abstract

An internal combustion engine system includes an engine and an aftertreatment system that is connected to the engine to receive exhaust flow from the engine. The aftertreatment system includes a passive storage device for passively storing NO x and/or hydrocarbons produced by the engine during cold start and low temperature operating conditions, and a NO x reduction catalyst downstream of the passive storage device for receiving the NO x released from the passive storage device when temperature conditions in the exhaust flow and/or NO x reduction catalyst are above an effective temperature for NO x reduction. Diagnostics of the passive storage device and/or a sensor downstream of the passive storage device are contemplated that are based at least in part on an expected sensor output in response to a storage mode of operation or a release mode of operation of the passive storage device. Furthermore, reductant injection control is provided in response to a NO x amount released from the passive storage device.

What is claimed is: 
     
         1 . A method, comprising:
 operating an internal combustion engine to produce an exhaust flow to an aftertreatment system including at least a passive storage device and a NO x  reduction device downstream of the passive storage device;   storing NO x  from the exhaust flow with the passive storage device during a NO x  storage mode of operation that occurs when the exhaust flow is in a low temperature condition;   releasing NO x  from the passive storage device in a NO x  release mode of operation when the NO x  reduction device is above an effective reduction temperature threshold for reducing NO x  across the NO x  reduction device;   determining a differential between an oxygen amount downstream of the passive storage device and an oxygen amount upstream of the passive storage device; and   providing a system output in response to the differential.   
     
     
         2 . The method of  claim 1 , further comprising:
 determining whether the passive storage device is in the NO x  storage mode of operation or the NO x  release mode of operation;   in response to the mode of operation, determining an expected differential between the oxygen amount upstream of the passive storage device and the oxygen amount downstream of the passive storage device; and   wherein providing the system output includes diagnosing a fault condition of the passive storage device in response to the determined differential deviating from the expected differential by more than a threshold amount.   
     
     
         3 . The method of  claim 1 , wherein determining the differential includes measuring an oxygen amount downstream of the passive storage device and measuring an oxygen amount upstream of the passive storage device. 
     
     
         4 . The method of  claim 3 , wherein measuring the oxygen amount downstream of the passive storage device includes determining an oxygen component of an output of a NO x  sensor downstream of the passive storage device. 
     
     
         5 . The method of  claim 4 , wherein measuring the oxygen amount upstream of the passive storage device includes measuring the oxygen amount with an oxygen sensor. 
     
     
         6 . The method of  claim 4 , wherein measuring the oxygen amount upstream of the passive storage device includes determining the oxygen amount from one or more operating parameters of the engine. 
     
     
         7 . The method of  claim 1 , wherein determining the differential includes measuring a difference between an oxygen amount downstream of the passive storage device and an oxygen amount upstream of the passive storage device. 
     
     
         8 . The method of  claim 1 , wherein the system output is operating the internal combustion engine to induce one of the NO x  storage mode of operation and the NO x  release mode of operation of the passive storage device. 
     
     
         9 . The method of  claim 8 , further comprising:
 determining an expected output of a NO x  sensor downstream of the passive storage device in response to the induced mode of operation of the passive storage device; and   determining a fault condition of the NO x  sensor in response to a measured output of the NO x  sensor deviating from the expected output by more than a threshold amount.   
     
     
         10 . The method of  claim 1 , wherein the NO x  reduction device is a selective catalytic reduction (SCR) catalyst and the aftertreatment system includes a reductant source operationally to provide an ammonia based reductant upstream of the SCR catalyst and downstream of the passive storage device. 
     
     
         11 . The method of  claim 1 , wherein providing the system output includes at least one of modulating a NO x  output of the engine and modulating a temperature of the exhaust flow in response to the differential. 
     
     
         12 . A method, comprising:
 operating an internal combustion engine to produce an exhaust flow to an aftertreatment system including at least a passive storage device and a NO x  reduction device downstream of the passive storage device;   storing hydrocarbons from the exhaust flow with the passive storage device during a hydrocarbon storage mode of operation of the PSD that occurs when the exhaust flow is in a low temperature condition;   oxidizing hydrocarbons from the passive storage device in a hydrocarbon release mode of operation of the passive storage device that occurs when the passive storage device is above a light-off temperature;   determining a differential between an air-fuel ratio downstream of the passive storage device and an air-fuel ratio upstream of the passive storage device; and   providing a system output in response to the differential.   
     
     
         13 . The method of  claim 12 , further comprising:
 determining whether the passive storage device is in the hydrocarbon storage mode of operation or the hydrocarbon release mode of operation;   in response to the mode of operation, determining an expected differential between the air-fuel ratio upstream of the passive storage device and the air-fuel ratio downstream of the passive storage device; and   wherein providing the system output includes diagnosing a fault condition of the passive storage device in response to the determined differential deviating from the expected differential by more than a threshold amount.   
     
     
         14 . The method of  claim 12 , wherein determining the differential includes measuring a difference between an oxygen and hydrocarbon amount downstream of the passive storage device and an oxygen and hydrocarbon amount upstream of the passive storage device. 
     
     
         15 . The method of  claim 14 , wherein the oxygen amount downstream of the passive storage device is determined by an oxygen component of an output of a NO x  sensor downstream of the passive storage device. 
     
     
         16 . The method of  claim 15 , wherein the oxygen amount upstream of the passive storage device is determined by an oxygen sensor. 
     
     
         17 . A method, comprising:
 operating an internal combustion engine to produce an exhaust flow to an aftertreatment system including at least a passive storage device and a NO x  reduction device downstream of the passive storage device;   storing NO x  from the exhaust flow with the passive storage device during a NO x  storage mode of operation of the passive storage device that occurs when the exhaust flow is in a low temperature condition;   releasing NO x  from the passive storage device in a NO x  release mode of operation of the passive storage device that occurs when the NO x  reduction device is above an effective reduction temperature threshold for reducing NO x  across the NO x  reduction device;   determining a NO x  amount released from the passive storage device during the NO x  release mode of operation with a NO x  sensor between the passive storage device and the NO x  reduction device; and   injecting a reductant amount into the exhaust flow upstream of the NO x  reduction device in response to the NO x  amount released.   
     
     
         18 . The method of  claim 17 , further comprising modulating a NO x  output of the engine in response to the NO x  amount released. 
     
     
         19 . The method of  claim 17 , further comprising:
 determining whether the passive storage device is in the NO x  storage mode of operation or the NO x  release mode of operation in response to a differential between an oxygen amount released from the passive storage device and an oxygen amount upstream of the passive storage device;   in response to the mode of operation, determining an expected differential between the oxygen amount upstream of the passive storage device and the oxygen amount released by the passive storage device; and   diagnosing a fault condition of the passive storage device in response to the determined differential deviating from the expected differential by more than a threshold amount.   
     
     
         20 . The method of  claim 19 , wherein the oxygen amount downstream of the passive storage device is determined by an oxygen component of an output of a NO x  sensor downstream of the passive storage device. 
     
     
         21 . The method of  claim 20 , wherein the oxygen amount upstream of the passive storage device is determined by an oxygen sensor. 
     
     
         22 . The method of  claim 17 , further comprising determining an expected NO x  amount to be released during the NO x  release mode of operation, and determining a fault condition for the NOx sensor in response to a measured NO x  amount by the NO x  sensor deviating from the expected NO x  amount by more than a threshold amount.